1. Field of the invention
This invention relates generally to implantable prostheses for human joint replacement, and relates more particularly to implantable prostheses that are not readily visible in x-ray radiographs and therefore require a radiographic marker.
2. Background information
Implantable orthopedics prostheses for human joint replacement are sometimes composed of materials which are substantially transparent to x-rays and which therefore do not show well on radiographs of the implanted prosthesis. One such material is high-density polyethylene which is often used as a bearing surface in orthopedic prostheses.
It is sometimes desirable to fashion an orthopedic implant entirely from polyethylene. Examples of such prostheses are all-poly cemented acetabular cups, and all-poly cemented shoulder glenolds. To permit radiographic examination of all-poly prostheses once implanted, it is known to provide a wrap of wire about the periphery of the prothesis. The wire is substantially opaque to x-rays and therefore will be easily visible on a radiographic view of the implanted prosthesis.
One known arrangement for providing a radiographic marker wire on, for example, an acetabular cup, involves wrapping a wire about the periphery of the cup near the opening such that the wire is received in an annular groove in the polyethylene material of which the cup is made. The ends of the wire are provided with a 90.degree. bend and are received in radially inwardly directed holes in the outer surface of the polyethylene cup. Engagement of the bent ends of the radiographic marker wire with the receiving holes of the cup prevent the wire from dislodging and becoming unwrapped.
As one can readily appreciate, the length of the marker wire must be precision cut to length so that the ends properly engage the holes when the wire is wrapped about the circumference of the cup. Furthermore, each size or diameter of acetabular cup requires a correspondingly sized marker wire, which multiplies the number of components that must be stocked in order to assemble all-poly prostheses of various sizes. It is also readily apparent that assembling the marker wire to the prosthesis can be a tedious and relatively time consuming operation.
It would be desirable to provide an all-poly orthopedic prosthesis that can be manufactured in different sizes without requiring a different sized radiographic marker for each prosthesis. It would also be desirable to provide an all-poly orthopedic prosthesis to which the radiographic marker can be easily and quickly attached.